A Kirby is not good for everyone
Some people are too weak to carry the heavy machine, of course, they put wheels on them so they will roll so this makes it much easier.
Though Kirbys are not that much heavier than other machines on the market this seems to be what the detractors zero in on when they don't have anything else negative to say.
A Hoover Wind Tunnel self-propelled weighs in at around 18lbs. A Dyson at around 18 lbs, a Rainbow at around 26 lbs, a Lux with power nozzle at around 25 lbs, a Simplicity Synergy at around 20 lbs. But those extra two or three pounds that a Kirby weighs is more than some can handle.
Noise is relative, but I do perceive the G series Kirbys to be a higher pitched noise than some of the older Generations. However, the previously mentioned Hoover is sometime perceived to be much louder, as with the Synergy. Now if you want a silent machine I would suggest you go with a central vac or maybe a Lux Guardian Platinum.
For cleaning abilities the previously mentioned machines are all good at what they do. If you want an upright with good cleaning ability, less weight and lower noise levels try a Sanitaire blue line with disposable bag.
*Mentioned weights are from memory so if I am off, I have no doubt someone will correct me, but you get the point.